The invention relates, in general, to the use of hard facing materials in tool joint construction and particularly relates to a method of improving and enhancing the service life of a tool joint which includes hard facing material.
The use of hard facing materials, such as tungsten carbide particles to form a hardened surface at a tool joint to increase wear resistance, has been disclosed in U.S. Pat. No. 3,989,554 issued Nov. 2, 1976 and in the History of Oil Well Drilling by J. E. Brantly, published in 1971 by the Book Division of Gulf Publishing Company, Houston, Tex. As apparatus and method for hardening the surface of a tool joint is also shown in Mexican Pat. No. 76008, granted in 1964 to the present inventor.
Such hard facing of a tool joint on a drill pipe greatly improved the wear resistance of the tool joint during use of the pipe in a well hole for petroleum products. In about the last ten years or so, drilling for geothermal resources has greatly increased. Drilling conditions for geothermal resources are quite different from petroleum drilling conditions in that the drill pipe is required to operate in a well hole in the presence of dry superheated steam, temperatures of from 250.degree. F. and above with total dissolved solids of from 2,000 ppm to 200,000 ppm, and under well conditions including 100,000-200,000 pounds per hour of stream by mass weight. Under such geothermal drilling conditions, the drill pipe and tool joints and tool collars thereon are subjected to much more severe erosion conditions and the number of times the drill pipe can be used is severely limited. Because the tool joint has an outer diameter greater than the normal outer diameter of the length of pipe and is provided with an elevator shoulder having a taper of 18.degree. to cooperate with pipe slips and clamps during running in and running out of the pipe with respect to the well hole, severe erosion and wear occurred on the elevator shoulders and on the cylindrical surface of the tool joint. Hard banding with tungsten carbide particles on the cylindrical surface and partially on the tapered surface enhanced wear resistance at these areas; however, the hard banding was accomplished with weld beads which left an external surface of quite irregular and interrupted character. When such hard banded tool joint pipe was used in geothermal applications, the irregular, interrupted contour of the hard banding provided a rough external surface for contact with the well fluid. Such a rough surface presented a multitude of surface irregularities against which geothermal well pressure fluids impinged under high temperature and pressure conditions which resulted in rapid deterioration and erosion of the hard banded weld metal and sometimes undercut adjacent softer pipe metal at the tool joint. Loss of metal at the tool joint substantially weakened the tool joint and made the pipe length nonavailable for use.